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authorJosef Bacik <josef@redhat.com>2011-07-18 21:21:35 +0400
committerAl Viro <viro@zeniv.linux.org.uk>2011-07-21 04:47:56 +0400
commit982d816581eeeacfe5b2b7c6d47d13a157616eff (patch)
tree1f1cb5725646e9de13969c8894b26ab3d5e3102e /Documentation/filesystems/porting
parentb4d5b10fb2e3a4327838c07d8ebd9e350fcc133d (diff)
downloadlinux-982d816581eeeacfe5b2b7c6d47d13a157616eff.tar.xz
fs: add SEEK_HOLE and SEEK_DATA flags
This just gets us ready to support the SEEK_HOLE and SEEK_DATA flags. Turns out using fiemap in things like cp cause more problems than it solves, so lets try and give userspace an interface that doesn't suck. We need to match solaris here, and the definitions are *o* If /whence/ is SEEK_HOLE, the offset of the start of the next hole greater than or equal to the supplied offset is returned. The definition of a hole is provided near the end of the DESCRIPTION. *o* If /whence/ is SEEK_DATA, the file pointer is set to the start of the next non-hole file region greater than or equal to the supplied offset. So in the generic case the entire file is data and there is a virtual hole at the end. That means we will just return i_size for SEEK_HOLE and will return the same offset for SEEK_DATA. This is how Solaris does it so we have to do it the same way. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'Documentation/filesystems/porting')
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1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index 0eeb3954dea3..6b96773e27cb 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -411,3 +411,13 @@ to some pointer to returning that pointer. On errors return ERR_PTR(...).
argument; instead of passing IPERM_FLAG_RCU we add MAY_NOT_BLOCK into mask.
generic_permission() has also lost the check_acl argument; if you want
non-NULL to be used for that inode, put it into ->i_op->check_acl.
+
+--
+[mandatory]
+ If you implement your own ->llseek() you must handle SEEK_HOLE and
+SEEK_DATA. You can hanle this by returning -EINVAL, but it would be nicer to
+support it in some way. The generic handler assumes that the entire file is
+data and there is a virtual hole at the end of the file. So if the provided
+offset is less than i_size and SEEK_DATA is specified, return the same offset.
+If the above is true for the offset and you are given SEEK_HOLE, return the end
+of the file. If the offset is i_size or greater return -ENXIO in either case.